Metal coating compositions prepared from aqueous dispersions of carboxylic acid resin and an aliphatic polyamine

ABSTRACT

Metal surfaces are coated with an aqueous dispersion containing a water dispersible carboxylic acid containing resin and aliphatic polyamine.

United States Patent [1 1 Hekal et 'al,

Sept. 9, 1975 METAL COATING COMPOSITIONS PREPARED FROM AQUEOUS DISPERSIONS OF CARBOXYLIC ACID RESIN AND AN ALIPHATIC POLYAMINE Inventors: Ihab M. Hekal, Downers Grove;

Raymond G. Chelton, Chicago, both of I11.

Assignee: Continental Can Company, Inc.,

New York, N.Y.

Filed: Sept. 10, 1973 Appl. No.: 395,820

Related US. Application Data Continuation-impart of Set. No. 301,022, Oct. 26, 1972.

US. Cl. 260/29.6 N; 260/296 M; 1 17/95;

117/97; 117/132 A Int. Cl. C03C 17/00; B32B 15/08 Field of Search 260/296 N, 29.6 M, 29.6 HN

References Cited Primary Examiner-Melvin Goldstein Assistant ExaminerPeter Kulkosky Attorney, Agent, or Firm-Pau1l Shapiro; Joseph E. Kerwin; William A. Dittmann [57] ABSTRACT Metal surfaces are coated with an aqueous dispersion containing a water dispersible carboxylic acid containing resin and aliphatic polyamine.

11 Claims, No Drawings I METAL COATING COMPOSITIONS PREPARED FROM AQUEOUS DISPERSIONS OF CARBOXYLIC ACID RESIN AND AN ALIPI-IATIC POLYAMINE This application is a continuation-in-part of our copending application Ser. No, 301,022. filed Oct. 26, 1972.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is related to the coating of metal articles. and more particularly to coating metal articles with aqueous dispersions of carboxylic acid containing resins.

2. The Prior Art In the manufacture of metal containers, a protective synthetic resin coating is applied to the interior of the container, The synthetic resins which are employed for coating the interior of the metal container are generally heat-curable, resinous materials which are applied in the form or a solution or dispersion in a volatile organic solvent. The wet-coated metal surface is passed through an oven in which hot air is circulated to evaporate the solvent and to cure the coating material to the required hardness. The removal of the organic solvent creates an air pollution problem which many present day communities will not tolerate. k

Among the various methods which have been proposed to avoid the use of organic solvents in preparing synthetic resin coatings for metal surfaces is to formulate the coating as an aqueous dispersion.

Aqueous dispersions of polymers having reactive carboxylic acid groups and heat curable, thermosetting resins have been preposed by the art as metal coatings, e.g. US. Pat. No. 2,902,390. US. Pat. No. 2,954,358, US. Pat. No. 3,053,693, US. Pat. No. 3,094,435, US. Pat. No. 3.117.227 1.1.5. Pat. No. 3,378,477, US. Pat. No. 3,403,088, US. Pat. No. 3,466,347 and Br. Pat. No. 1,271,572. These coating materials have not found wide commercial application in the beverage container industry as many of these coatings are not sufficinently inert to the packaged product. For example, malt beverages such as beer and ale are especially sensitive to container coatings and many coating materials are rejected because contact with malt beverages, even for short periods of time, causes the beverage to lose clarity and deteriorate into a cloudy product which is unacceptable to the consumer.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided, dispersed in an aqueous medium, a coating composition for application to metal surfaces to provide a coating film inert to malt beverages which coating composition is comprised of a mixture of carboxylic acid cin taining resinand an aliphatic polyamine.

As will hereinafter be illustrated, the aqueous coating compositions of the present invention when applied to metal surfaces such aluminum provide a coating film of sufficient product inertness that the coating compositions can be applied to the interior of containers used for the packaging of malt beverages.

PREFERRED EMBODIMENTS The term carboxylic acid containing resin" as used herein includes within its meaning copolymers of a-olefins with an ethylenically unsaturated carboxylic acid.

2 The a-olefins employed in preparing the carboxylic acid containing resin are oz-olefins which have the general formula RCH=CH wherein R is either a hydrogen or a alkyl group having from 1 to 8 carbon atoms. Typical examples of suitable olefins include ethylene, propylenc, butene-l, and 3-methylbutene-l.

The ethylenically unsaturated carboxylic acid component of the carboxylic acid] resin is an a,B-ethylenically' unsaturated carboxylic acid having from 3 to 8 carbon atoms. Examples of such acids are acrylic acid, methacrylic acid,-ethacrylic acid, itaconic acid, maleic acid, fumarate, ethyl hydrogen fumarate, and maleic anhydride. In the preparation of the compositions of the present invention carboxylic acid containing resins prepared from acrylic acid and methacrylic acid are preferred.

The concentration of the Ct-OICfIn in the acidic copolymer is in the range of about 60 to about 90 weight percent and the concentration of acidic monomer is from about 10 weight percent to about 40 weight percent, and preferably, from 15 to 30 Weight percent.

The carboxylic acid containing resin need not necessarily be a two component polymer. Thus. although the olefin content of the acid copolymer should be about 60 to about 90 weight percent, more than one olefin can be employed to provide the hydrocarbon nature of the copolymer base. Additionally, any third copolymerizable monomer can be employed in combination with the olefin and the ethylenically unsaturated acid comonomer. The scope of copolymers suitable for use in the present invention is illustrated by the following exanv ples: ethylene/acrylic acid copolymers, ethylene/methacrylic acid copolymers, ethylcne/itaconic acid copolymers, ethylene/malcic acid copolymers, ethylene/acrylic acid/methyl methacrylate copolymers. ethylene methacrylic acid/ethyl acrylate copolymers, ethylene/propylene/acrylic acid copolymers, ethylene/- vinyl chloride/acrylic acid copolymers, polyethylene/acrylic acid graft copolymers, polyethylene/methacrylic acid graft copolymers, polypropyleneacrylic acid graft copolymers and polypropylene/methacrylic acid graft copolymers,

The term carboxylic acid resin also includes within its meaning copolymers of a-olefin with an ethyleni cally unsaturated carboxylic acid in which about 5 to about percent by weight of the carboxylic acid groups have been neutralized by metal ions. These resins are referred to in the art as ionomer resins."

The metal ions used to obtain partial neutralization of the olefin/carboxylic acid copolymer will generally have a valence of l to 3 inclusive and fall in Groups 1 (A and B) and 11 (A and B) and the transititon elements of the PeriodicTable. Illustrative of ionomer resins which may be employed in the practice of the present invention are the alkali metal salts of ethylene/acrylic acid and ethylene/methacrylic acid copolymers containing the cations Na+, 14+, Li+, the alkaline earth salts of ethylene/acrylic acid and ethylene/methacrylic acid copolymers containing the cations Ca-1l, Ba+l-. Mg++, Sr-H- and the zinc salts of these copolymers. Of these, the alkali metal salts are preferred in the practice of the present invention.

The preparation of ionomer resins is disclosed in US.

the present invention havesufficient molecular weight to have a melt index of 100 or less and preferably the melt indexof the ionomer resin ranges from 5 to 50 as determined by the procedures set forth in ASTM D- In preparing the aqueous coating'compositions of the present invention the free acid content of the ionomer resin generally ranges from about 5 to about 20 percent by weight. Such ionomer resins are commercially available from the El. Dupont De' Nemours Company, lnc., Electrochemicals Department. Wilmington, Delaware under the trademark ELVAXD-l265. ELVAX 1265 is an ethylene/methacrylic acid copolymer partially neutralized with sodium ion having a free acid content greater than l3 percent by weight and generally about 14 to 18 percent by weight and a melt index of IO to 30.."

The aliphatic polyamines used in combination with the carboxylic acid containing resins to prepare the coating compositions of the present invention include aliphatic polyamines such as hexamethylene tetramine and polyamines having the general formula NH (C H NH) ,C H NH wherein .v is an integer from to 20, and preferably 0 to 10. Exemplary of these polyamines are ethylene diamine. dictbylene triaminc. triethylenc tetramine, tetraethylcnc pentamine. pentaethylene hexamine. hcxaethylene heptamine, heptaethylene octamine octaethylcne nonamine and nonaethylene decamine.

The aqueous dispersions used in the practice of the present invention are prepared by dispersing the carboxylic acid containing resin and polyamine in the aqueous liquid system wherein the amount of the polyamine incorporated in the dispersion is dependent on the acid content of the resin and is generally that amount which is sufficient to completely react with the free acid of the carboxylic acid containing resin. For resins having a free acid content of from 5 to 20 percent by weight, the coating compositions of the present invention are comprised of 75 to 90% by weight of the carboxylic acid containing resin and about l() to 25% by weight and preferably about to about by weight of the polyamine. Concentrations of polyaminc in excess of by weight are to be avoided as the application to metal surfaces of coating compositions containing polyamines in concentrations in excess of 2571 by weight results in a rough, discontinuous and therefore unacceptable coating film. Concentrations of polyaminc of less than lO'Yr by weight in the coating compositions results; in a soft coating film that has very poor abrasion resistance which will scratch easily during container handling in the manufacturing process. 7

The aqueous coating dispersions of the present invention may also contain fillers, dyes, pigments, surfactants. anti-foam agents, plasticizers, stabilizers, antioxidants in accordance with conventional practice in preparing coatingcompositons. I

The coating compositions of the present invention can be,satisfactoril'y applied to metal surfaces by any of the c'onyentional methods employed by the coating industry; However for coating the walls of metal contain.- ers, rinse coating is a preferred method. For general coating purposes, roll, spray and flow coating are also useful methods of application. After applying the coat- 450] for a period of about 1 to 10 minutes.

The preferred coating weight for coating the interior walls of metal containers with an adequately protective organic coating suitable for carbonated beverages is in the range of ().l to 5 milligrams of carboxylic acid containing resin coating per square inch of exposed metal surface.

The present invention is illustrated, but not limited, by the following examples.

EXAMPLE I A series of aqueous coating compositions were prepared having a 5% solids content composed of parts of ELVAX D1265, an ionomer resin, and 15 parts of a variety of aliphatic polyamines. The aqueous coating dispersions were coated on aluminum foil, and then baked for 4 minutes at an oven temperature of about 375F.

The inertncss of the coatings to malt beverages was evaluated by a turbidity test whereby the coated aluminum foil was inserted into a bottle of beer. the bottle scaled and then allowed to stand for 1 day at l30F followed by 1 day at F whereupon the beer was examined for signs of turbidity.

The results of the turbidity tests of aluminum foil coated with the ionomer resin-aliphatic polyaminc aqueous coating compositions is recorded in the Table below.

For purposes of contrast, as a control test. aluminum foil which had been coated in a manner similar to that of Example I but to which a nitrogen containing crosslinking agent outside the scope of the invention was substituted for the aliphatic polyamine components used in Example I were also subjected to the turbidity test. The results of these control tests (designated by *ZIM RHONITE RQ. N. N bis (mcthnxymcthyll uron "2W7, L'F 492. product of Rnhm and Haas "204; MMX3. product of Rohm and Haas By reference to the Table, it is immediately apparent that aluminum coated with ionomer resin dispersions having aliphatic polyamines incorporated therein in accordance with the present invention exhibit superior inertncss to beer when compared to aluminum coated with an ionomer dispersion in which a nitrogen containing compound other than an aliphatic polyaminc is employed in the coating dispersion.

EXAMPLE ll An aqueous coating composition was prepared having a 5% solids content composed of 85 parts of an ethylene/methacrylic acid copolymer containing about 1 3 to 18% by weight acid the copolymer being neutralized with an amine to an alkaline pH to effect dispersion thereof in the aqueous medium. To the dispersion was added l5 parts of diethylene triamine. The aqueous coating dispersion was coated on aluminum foil,

and then baked for 4 minutes of about 38S /4F.

The inertness of the coating to malt beverages was evaluated by the turbidity test of Example I. No turbidity was observed with aluminum foil coated with the ethylene/methacrylic aciddiethylene triamine coating composition.

What is claimed is:

l. A coating composition suitable for coating metal surfaces comprising an aqueous dispersion having disperscd therein a mixture of about 75 to 90% by weight of (l) a carboxylic acid containing olefin copolymer having reactive carboxyl groups prepared from about 60 to about 90 percent by weight of an a-olefin having the general formula RCH=CH wherein R is selected from the group having 1 to 8 carbon atoms and about to about 40 percent by weight of an a,B-ethylenically unsaturated carboxylic acid having 3 to 8 carbon atoms, and about 10 to percent by weight of (2) an aliphatic polyamine selected from the group consisting of hexamethylcne tetramine and amines of the general formula NH (C H,,NH) ,.C H.,NH it being an integer from 0 to 20, the amount of aliphatic polyamine in the mixture being sufficient to completely react with the reactive carboxyl groups of the carboxylic acid containing olefin copolymer.

2. The coating composition of claim 1 wherein the at an oven temperature a-olcfin is ethylene.

3. The coating composition of claim 1 wherein the ethylenically unsaturated carboxylic acid is selected from the group consisting of acrylic and methacrylic acidv 4. The coating composition of claim 1 wherein about 5 to about percent of the carboxylic acid groups are neutralized by metal ions.

5. The coating composition of claim 4 wherein the carboxylic acid groups of the olefin copolymer are neutralized with metal ions selected from the group consisting of alkali metal, alkaline earth and zinc ions.

6. The coating composition of claim 4 wherein the carboxylic acid groups are neutralized with sodium ions.

7. The coating composition of claim 1 wherein the aliphatic polyamine is ethylene diamine.

8. The coating composition of claim 1 wherein the aliphatic polyamine is diethylene triamine.

9. The coating composition of claim 1 wherein the aliphatic polyaminc is triethylcne tetramine.

10. The coating composition of claim 1 wherein the aliphatic polyamine is tetraethylene pentamine.

11. The coating composition of claim 1 wherein the mixture comprises 1 to about 45 percent by weight of the aqueous dispersion. 

1. A COATING COMPOSITION SUITABLE FOR COATING METAL SURFACES COMPRISING AN AQUEOUS DISPERSION HAVING DISPERSED THEREIN A MIXTURE OF ABOUT 75 TO 90% BY WEIGHT OF (1) A CARBOXYLIC ACID CONTAINING OLEFIN COPOLYMER HAVING REACTIVE CARBOXYL GROUPS PREPARED FROM ABOUT 60 TO ABOUT 90 PERCENT BY WEIGHT OF AN A-OLEFIN HAVING THE GENERAL FORMULA RCH=CH2 WHEREIN R IS SELECTED FROM THE GROUP HAVING 1 TO 8 CARBON ATOMS AND ABOUT 10 TO ABOUT 40 PERCENT BY WEIGHT OF AN A,B-ETHYLENICALLY UNSATURATED CARBOXYLIC ACID HAVING 3 TO 8 CARBON ATOMS, AND ABOUT 10 TO 25 PERCENT BY WEIGHT OF (2) AN ALIPHATIC POLYAMINE SELECTED FROM THE GROUP CONSISTING OF HEXAMETHYLENE TETRAMINE AND AMINES OF THE GENERAL FORMULA NH2(C2H4NH)XC2H4NH2, X BEING AN INTEGER FROM 0 TO 20, THE AMOUNT OF ALIPHATIC POLYAMINE IN THE MIXTURE BEING SUFFICIENT TO COMPLETELY REACT WITH THE REACTIVE CARBOXYL GROUPS OF THE CARBOXYLIC ACID CONTAINING OLEFIN COPOLYMER.
 2. The coating composition of claim 1 wherein the Alpha -olefin is ethylene.
 3. The coating composition of claim 1 wherein the ethylenically unsaturated carboxylic acid is selected from the group consisting of acrylic and methacrylic acid.
 4. The coating composition of claim 1 wherein about 5 to about 75 percent of the carboxylic acid groups are neutralized by metal ions.
 5. The coating composition of claim 4 wherein the carboxylic acid groups of the olefin copolymer are neutralized with metal ions selected from the group consisting of alkali metal, alkaline earth and zinc ions.
 6. The coating composition of claim 4 wherein the carboxylic acid groups are neutralized with sodium ions.
 7. The coating composition of claim 1 wherein the aliphatic polyamine is ethylene diamine.
 8. The coating composition of claim 1 wherein the aliphatic polyamine is diethylene triamine.
 9. The coating composition of claim 1 wherein the aliphatic polyamine is triethylene tetramine.
 10. The coating composition of claim 1 wherein the aliphatic polyamine is tetraethylene pentamine.
 11. The coating composition of claim 1 wherein the mixture comprises 1 to about 45 percent by weight of the aqueous dispersion. 